Screen content coding imposes new challenges for video compression technology because of its distinct signal characteristics compared with conventional natural videos. There appear to be a few promising techniques for the advanced screen content coding, e.g., pseudo string match, color palette coding, and intra motion compensation or intra block copy.
Among these techniques, pseudo string match shows the highest gain for lossless coding, but with significant complexity overhead and difficulties on lossy coding mode. The color palette coding is developed for screen content under the assumption that non-camera captured content typically contains a limited few distinct colors, rather than the continuous color tone in natural videos. Even though the pseudo string match and color palette coding methods showed great potential, intra motion compensation or intra block copy was adopted into the working draft (WD) version 4 and reference software of on-going HEVC range extension (HEVC RExt) for screen content coding. This is mainly due to the fact that the motion estimation and compensation approach has been studied extensively over decades, as well as its idea and practical implementation is fairly easy (especially for hardware).
However, the coding performance of intra block copy is bounded because of its fixed block structure partitions. On the other hand, performing block matching, something similar to motion estimation in intra picture, also brings up the encoder complexity significantly on both computing and memory access.